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Old 03-12-2013, 05:29 AM
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Tune the motor..

Use a good stock single points distributor with a 1962-1964 389 distributor cam (20 degrees mechanical advance, no plastic bushing), stock Delco coil with a 1.5 ohm resister and a set of Accel points...
Limit the vaccum advance to 10 degrees by soldering the arm and have the springs set to start advancing at 900-1000 rpms with full advance at 2200-2500...

Get a Quadrajet carb and build it to Cliffs specs... Cliffs High Performance Quadrajets :: Qjet Carburetor Rebuild Kits, Parts, Quadrajet Rebuilding, Quadrajet Parts, Bushing Kits, Carb Tuning

Once you get the motor running decently check the compression..

Good luck....

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Old 03-12-2013, 11:22 AM
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First, all Pontiac heads "fit". "Fit" and "right" are two separate issues. Have you tried "race" gas to verify it's octane? Do that first. A couple gallons should do it.

Jim
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Old 03-12-2013, 03:59 PM
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Wallace shows the 6X - 8 heads coming in at 101 CCs. On a 455 that is well below 9 to 1. sounds like compression wont be the issue....
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Old 03-12-2013, 06:30 PM
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Quote:
Originally Posted by LATECH View Post
Wallace shows the 6X - 8 heads coming in at 101 CCs. On a 455 that is well below 9 to 1. sounds like compression wont be the issue....
Not w/6X-8 heads, it won't. But if they're 6X-4's, that's another story if they're seriously milled. Unmilled or w/just a light 'clean-up' cut on the decks w/FT pistons are OK on a 455 in my experience.

Hopefully he'll have more info for us.
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Old 03-12-2013, 10:41 PM
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@ bonneville462, thank you for the advice i am on a budget i only have the demon carb i have 3 other quadrajets but they are all in need of rejetting/rebuilding the demon works great except the secondaries need a new spring or diaphragm which is better for my budget...

@P-Body i get what your saying i read that they will both work fine and fit fine the 4s is 94cc and the 8's are 101 i believe then again its the internet so i dont believe it im still trying to determine which they are i cannot find either an 8 or 4 if i have the 4s is it possible to run them with the right tuning ? and i am gonna get race gas or brew it my self what octane should i make/find? 100+ or in the 90s? 91 is the highest pump gas around here.

@LATECH yea i have a feeling its somehwere in the timing and or air to fuel mixture.. the car starts up runs great at normal speeds and acceleration, temps good oil pressure is good, again im no expert still learning.

@cobalt the heads have been machined i believe .20 from the surface, and ported and polished matching the intake ports.. i got them for free so i dont know much i do know they came off a car with under 200 miles on the motor built with them so they arent beat to ****.
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Old 03-12-2013, 11:07 PM
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Heres a photo i had on my phone, just so you have a visual not that it will help but always nice to have an image! i will get better photos tomorrow, also i can post a few from start to where im at now as my first project .
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Old 03-12-2013, 11:29 PM
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take note that im a youngster doing what i can to get into hot rodding and building motors, on a minimum wage job as a cook. so that being said everything was kinda mix and matched, heads and intake came off someone else's project car, carb off another, power steeing pump off the original cadillac motor, block was a spur of the moment find/buy, alot of bone yard parts, throttle linkage is made from homedepot supplys . i did but new parts like the cam and roller rockers, gaskets nuts bolts hoses wires, electric fuel pump etc. this is why im running into these problems there was no guidelines or directions,i did get help from a friend/engine builder. he helps me here and there but its hard to keep up with him. going over it on here helps alot thanks for your guises help!
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Old 03-13-2013, 11:33 AM
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There's a good set of pics around showing where the secondary marking is on the 6X head. I don't have the link, but I believe Bill Creech does. Maybe he'll come along and see this.

If you look at the head from the side of the engine, there are three verticle ribs "cast in". Two to the left of center, one to the right. The one on the right is the one we're interested in. At the top, just below the valve cover, there's a "flat" machined onto the rib. The secondary code is stamped on that "flat".

If -4s and .020" was milled, they're down around 90 CCs, which is ideal for a 406 or 412 CID engine and 89 octane.

I would say a "mix" of 6 parts 91 and 4 parts 109 should do the trick...

Jim
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Old 03-13-2013, 02:54 PM
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I am posting a pic of a 6x-4 head I had been running on my 455, just for reference. it's pretty easy to find the stamping. it's on a flattened riser/boss/casting (not sure of the terminology here) above and just to the left of the center exhaust ports. Circled in red in the first pic, then zoomed in on the second.

--edit that 4 or 6 stamp may exist on another of the "ribs" on the head as Mr. P-Body described. I bet pontiac stamped wherever they had clean material available in the different years. I've seen these stampings where it appears that the die "bounced", i wonder if these were done by hand wherever they were finished? *shrug*
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Old 03-13-2013, 04:33 PM
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Quote:
Originally Posted by Mr. P-Body View Post
There's a good set of pics around showing where the secondary marking is on the 6X head. I don't have the link, but I believe Bill Creech does. Maybe he'll come along and see this.

Jim

Ask and you shall recieve. This is a picture of a 5C head, but the location of the stamps are the same:

I've got pics of other casting code and stamping locations, if you need them.

Bill
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Old 03-13-2013, 06:04 PM
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yea there is no stamp other then the date, 6x on the center port, and the gm i was just looking at my heads for 20 minutes inspecting ever crevasse! should i take a close up of them? if i do have the 4s can i still run with them or would i have to run only high octane becuase right now with normal driving conditions it will run no problem on 91 but as soon as i step on it... ping ping ping..
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Old 03-13-2013, 07:02 PM
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okay i found it! i had sanded the entire block and heads lightly and painted it so it kinda got filled in with the paint..
So they are the 8s..

so this is where im at:

Heads - 6x "8" machined ported & polished .20

Cam - .510

Bottom end - Stock

Timing - 20 initial 27 Total advance not working on distributor

Power valve - 3.5 secondaries not working properly

Fuel pressure - 7-8psi

Temp - average 180 degrees

Idle - 600rpm

Gas - 91 octane

is that enough to narrow it down?
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Old 03-13-2013, 07:21 PM
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Thanks, Bill.

I'm thinking you should have a 65 power valve in there, not a 35. It COULD be leaning out on "tip-in", which can induce detonation. 35 means the valve opens at 3 1/2" of vacuum, 65 = 6.5". Bringing the fuel in "sooner" can help a lot.

Was the cam "degreed"? What is the intake centerline? I've seen some pretty bad detonation with cams when installed too far "advanced". In one case, it was an XE262H and was at 98 (should be 106). It stretch the chain badly, and had two distinct "burn lines" in the cylinders, before it beat the rod bearings out, all in less than 500 miles. The owner wasn't "savvy" and didn't realize the pinging would hurt things. He knows now!

A compression test could be revealing, as well. Cylinder pressure over about 180 lbs. is prone to detonation in Pontiacs, no matter the static ratio. You will undoubtedly hear "success stories" with more, but this is a good "line". A typical 9:1 engine with a mild performance cam will generate around 170 lbs. A stock 400 in '69 would push 210, easy. They were advertised at 10.75:1, but I've found them closer to 10.5:1, and the later "10.5:1" engines were closer to 10:1.


Jim
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Old 03-13-2013, 07:30 PM
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So the power valve can cause it to lean out when excessive acceleration ? and a 65 would solve that?
and the cam was just put in straight not degreed. and im not sure what a intake centerline means..

haha thats what im trying to avoid this thing is my baby!

and okay, where do you think im at compression ratio wise?
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Old 03-13-2013, 11:29 PM
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Quote:
Originally Posted by PontiLac View Post
where do you think im at compression ratio wise?
Removing 0.020" will reduce the chamber volume by about 4cc or so. But not knowing how far down the piston is at TDC or the head gasket thickness, it's hard to say exactly.

Given an ideal 0.040" quench, the CR is about 9.4:1. But it's likely going to be less than that. How much less depends on the things I mentioned just now, but I suspect it will fall somewhere between 9:1 and 9.4:1. This is w/aftermarket true FT pistons having a 5cc valve relief volume. Stock type pistons have a larger volume than true FT pistons, so using them the CR will be lower.
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